U.S. patent application number 10/662447 was filed with the patent office on 2004-05-13 for motor power supply and method of controlling the same.
This patent application is currently assigned to Samsung Electronics Co., Ltd.. Invention is credited to Youm, Jang-Hyoun.
Application Number | 20040090807 10/662447 |
Document ID | / |
Family ID | 32226263 |
Filed Date | 2004-05-13 |
United States Patent
Application |
20040090807 |
Kind Code |
A1 |
Youm, Jang-Hyoun |
May 13, 2004 |
Motor power supply and method of controlling the same
Abstract
A motor power supply for and a method of operating a poly-phase
AC motor with power provided from an AC power source through a
DC-conversion circuit and an inverter. An output voltage of the
DC-conversion circuit is sensed and a controller controls an inrush
current limiting resistance to be selectively bypassed according to
a first value of the output voltage and controls a pair of switches
in an overvoltage protection circuit to return energy stored in the
DC-conversion circuit to the AC power source according to second
and third values of the output voltage. An operation of the
switches is synchronously controlled according to a phase of the AC
power source. The overvoltage protection circuit eliminates an
overvoltage in the DC-conversion circuit due to energy regenerated
by the motor and passed through the inverter to the DC-conversion
circuit.
Inventors: |
Youm, Jang-Hyoun; (Suwon
City, KR) |
Correspondence
Address: |
STAAS & HALSEY LLP
SUITE 700
1201 NEW YORK AVENUE, N.W.
WASHINGTON
DC
20005
US
|
Assignee: |
Samsung Electronics Co.,
Ltd.
Suwon City
KR
|
Family ID: |
32226263 |
Appl. No.: |
10/662447 |
Filed: |
September 16, 2003 |
Current U.S.
Class: |
363/132 |
Current CPC
Class: |
Y02P 80/10 20151101;
H02M 7/5387 20130101; H02M 1/32 20130101; H02M 7/219 20130101 |
Class at
Publication: |
363/132 |
International
Class: |
H02M 007/5387 |
Foreign Application Data
Date |
Code |
Application Number |
Nov 8, 2002 |
JP |
2002-69167 |
Claims
What is claimed is:
1. A motor power supply comprising: a DC-conversion part which
converts AC power from an AC power input part into DC power; an
inrush current limiting resistance provided between the AC power
input and the DC-conversion part; an overvoltage-protection
switching part provided between the inrush current limiting
resistance and the DC-conversion part; a sensor which senses an
output voltage of the DC-conversion part; and a controller which
switches the overvoltage-protection switching part On/Off to return
energy stored in the DC-conversion part to the AC power input part
through the inrush current limiting resistance when the output
voltage of to the DC-conversion part is higher than a predetermined
voltage.
2. The motor power supply according to claim 1, wherein: the
DC-conversion part comprises a pair of capacitors which are
respectively charged with positive and negative voltages from the
AC power.
3. The motor power supply according to claim 2, wherein: the
overvoltage-protection switching part comprises a pair of field
effect transistors.
4. The motor power supply according to claim 3, wherein: the
controller switches On/Off the overvoltage-protection switching
part to discharge at least one of the capacitors when the output
voltage reaches a predetermined overvoltage limit.
5. The motor power supply according to claim 4, wherein: the sensor
comprises a comparator which determines whether the output voltage
reaches the predetermined overvoltage limit.
6. The motor power supply according to claim 5, further comprising:
a relay which selectively bypasses the limiting resistance.
7. The motor power supply according to claim 5, wherein the
controller switches the relay to bypass the resistance when the
output voltage reaches a predetermined voltage value, and switches
the relay so that the resistance is not bypassed when the output
voltage reaches the predetermined overvoltage limit.
8. A method of controlling a motor power supply comprising an AC
power input part, a DC-conversion part which converts AC power from
the AC power input part into DC power, an inrush current limiting
resistance provided between the AC power input part and the
DC-conversion part, and an overvoltage-protection switching part
connected with the DC-conversion part in parallel, the method
comprising: charging the DC-conversion part when power is initially
supplied via the inrush current limiting resistance; sensing a
voltage charged in the DC-conversion part; and switching the
overvoltage-protection switching part alternately On/Off when the
sensed voltage is higher than a first predetermined voltage value,
to reduce the voltage charged in the DC-conversion part by
returning energy stored in the DC-conversion part toward the AC
power input part.
9. The method according to claim 8, wherein: the motor power supply
further comprises a relay which selectively bypasses the inrush
current limiting resistance, and the method further comprises:
bypassing the inrush current limiting resistance when the voltage
charged in the DC-conversion part reaches a second predetermined
voltage value, so that the AC power input part and the
DC-conversion part are directly connected.
10. The method according to claim 9, further comprising: stopping
the bypassing of the current limiting resistance when the voltage
charged in the DC-conversion part is greater than the first
predetermined voltage value.
11. The method according to claim 9, further comprising: stopping
the bypassing of the current limiting resistance when the voltage
charged in the DC-conversion part is less than the second
predetermined voltage value.
12. The method according to claim 8, wherein the switching of the
overvoltage-protection switching part alternately On/Off comprises:
switching the overvoltage-overvoltage protection switching part On,
where the voltage charged in the DC-conversion part becomes greater
than a second predetermined value; and switching the
overvoltage-overvoltage protection switching part OFF, where the
voltage charged in the DC-conversion part becomes less than the
first predetermined value.
13. The method according to claim 10, wherein the switching of the
overvoltage-protection switching part alternately On/Off comprises:
switching the overvoltage-overvoltage protection switching part On,
where the voltage charged in the DC-conversion part becomes greater
than a second predetermined value; and switching the
overvoltage-overvoltage protection switching part OFF, where the
voltage charged in the DC-conversion part becomes less than the
first predetermined value.
14. A motor power supply for supplying an AC motor with power
provided from an AC power source through an inverter, the motor
power supply comprising: a DC conversion circuit which converts
power from the AC power source to DC power and outputs the DC power
to the inverter; a sensor which senses a voltage at an output of
the DC conversion circuit; an overvoltage protection circuit which
returns energy from the DC conversion circuit to the AC power
source if the sensed output voltage exceeds a first predetermined
value.
15. The motor power supply according to claim 14, further
comprising: a controller which controls the overvoltage protection
circuit in response to the sensed voltage.
16. The motor power supply according to claim 15, wherein: the
overvoltage protection circuit comprises at least one switch which
selectively forms a current path between the output of the DC
conversion circuit and the AC current source; and the controller
switches the at least one switch synchronously with a phase of the
AC power source to return the energy from the DC conversion circuit
to the AC power source.
17. The motor power supply according to claim 16, wherein the at
least one switch is a field effect transistor (FET).
18. The motor power supply according to claim 17, wherein a diode
formed integrally with the FET forms a part of the DC conversion
circuit.
19. The motor power supply according to claim 14, wherein: the DC
conversion circuit comprises a capacitance circuit which stores the
energy; the overvoltage protection circuit comprises first and
second switches, the first switch selectively forming a first
current path between a first end of the capacitance and the AC
current source and the second switch selectively forming a current
path between a second end of the capacitance and the current
source; and the controller switches the first and second switches
synchronously with the AC power source to return the energy from
the DC conversion circuit to the AC power source.
20. The motor power supply according to claim 19, wherein: the AC
power source comprises outputs L1 and L2; the controller switches
the first switch where a voltage at L1 is greater than a voltage at
L2 and switches the second switch where the voltage at L2 is
greater that the voltage at L1.
21. The motor power supply according to claim 14, wherein: the
motor power supply further comprises: a resistance selectively
connectable between the AC power source and the DC conversion
circuit, and a controller; and the overvoltage protection circuit
comprises at least one switch which selectively forms a current
path between the output of the DC conversion circuit and the AC
current source; wherein, the controller: switches the at least one
switch synchronously with a phase of the AC power source to return
the energy from the DC conversion circuit to the AC power source,
and controls the resistance to be connected between the AC power
source and the DC conversion circuit where the output voltage is
less than a second predetermined value or greater than the first
predetermined value.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application claims the benefit of Korean Patent
Application No. 2002-69167, filed Nov. 8, 2002, in the Korean
Intellectual Property Office, the disclosure of which is
incorporated herein by reference.
BACKGROUND OF THE INVENTION
[0002] 1. Field of the Invention
[0003] The present invention relates to a power supply for a motor,
and more particularly, to a power supply for a motor and a method
of supplying power to the motor, which improve energy
efficiency.
[0004] 2. Description of the Related Art
[0005] A three-phase motor is the kind of motor in which coils are
spaced about a rotor of the motor and are connected to operate from
a three phase power source . As shown in FIG. 6, a motor power
supply 100 for the three-phase motor is employed to output a
three-phase voltage to drive a motor 117, and comprises an
alternating current (AC) power supply input part 101 which receives
a commercial AC power, such as for example, 110/220V, a soft
charging circuit 103 which prevents an excessive inrush current
from flowing when power is initially supplied, a direct current
(DC)-conversion circuit 106 which converts AC power into DC power,
an overvoltage-protection circuit 112 which protects the
DC-conversion circuit 106 from overvoltage, and an inverter 116
which converts the DC power into three-phase AC power having
various frequencies. The inverter 116 comprises a pulse width
modulation (PWM) part (not shown) which generates a PWM signal, and
a plurality of transistors which are switched on/off according to a
square waveform signal output from the PWM part. Further, the motor
power supply 100 comprises a micom (not shown) which controls an
output of the inverter 116 to be on/off by switching on/off the
transistors according to the PWM control signal, and controls a
rotation speed of the motor 117 by changing a frequency of the
output of the inverter 116.
[0006] The motor power supply 100 employs a rectifying circuit 105
and a capacitor circuit 107 which function as a voltage doubler,
when a voltage of 220 Vrms is needed and a voltage of 100.about.110
Vrms is input. In order to smoothly control the motor 117, the
DC-conversion capacitor circuit 107 should have sufficiently large
capacity. Therefore, when power is initially supplied, the
capacitors C.sub.DC1 and C.sub.DC2 of the DC-conversion capacitor
circuit 107 are charged, causing very high inrush current if the
current is not otherwise limited. The high inrush current is likely
to generate a current spike, thereby overloading the AC power input
and tripping a circuit breaker to break the power, affecting other
devices connected to the AC power input part, or shortening a life
span of the capacitors of the DC-conversion capacitor circuit
107.
[0007] The soft charging circuit 103 limits the inrush current. As
shown in FIG. 6, when power is initially supplied, a relay 102 is
in the state of being switched off, so that the capacitors
C.sub.DC1 and C.sub.DC2 are charged with a positive voltage passing
through an inrush current limiting resistor 104 and a diode D1 and
a negative voltage passing through the inrush current limiting
resistor 104 and a diode D2, respectively. A total voltage applied
to the pair of capacitors C.sub.DC1 and C.sub.DC2 in the
DC-conversion circuit will be referred to as V.sub.PN. When
V.sub.PN is equal to a charging stop voltage V1, the relay 102 is
switched on, so that the power from AC power input part 101 is
directly supplied to the diodes D1 and D2 in the rectifying circuit
105.
[0008] While the motor 117 operates, regenerative power may be
generated by the inverter 116 and supplied to the DC-conversion
circuit 106. When the capacitors C.sub.DC1 and C.sub.DC2 are
over-charged with the regenerative power, the
overvoltage-protection circuit 112 senses that V.sub.PN is higher
than a predetermined voltage (i.e., a critical overvoltage), and
switches on a transistor 109 of the overvoltage-protection circuit
112, to dissipate the regenerative power as heat energy through a
resistor 110 of the overvoltage-protection circuit 112.
[0009] However, in the conventional motor power supply, the
regenerative energy generated while the motor 117 operates is
wasted as the heat energy by the resistor 110 of the
overvoltage-protection circuit 112, thereby decreasing energy
efficiency. Further, in the conventional motor power supply 100,
there are needed the resistor 104 to limit the inrush current and
the resistor 110 to protect against the overvoltage, so that a size
of the motor power supply 100 is increased.
SUMMARY OF THE INVENTION
[0010] Accordingly, it is an aspect of the present invention to
provide a motor power supply and a method of controlling the same,
in which a regenerative energy which overloads a DC-conversion
circuit is used as an input energy, thereby enhancing energy
efficiency.
[0011] Additional aspects and/or advantages of the invention will
be set forth in part in the description which follows and, in part,
will be obvious form the description, or may be learned by practice
of the invention.
[0012] The foregoing and/or other aspects of the present invention
are achieved by providing a motor power supply comprising an AC
power input part, a DC-conversion part which converts AC power from
the AC power input part into DC power, an inrush current limiting
resistor selectively provided between the AC power input part and
the DC-conversion part, an overvoltage-protection switching part
provided between the inrush current limiting resistor and the
DC-conversion part which controls an output voltage of the
DC-conversion part; a sensor which senses the output voltage of the
DC-conversion part; and a controller which switches On and Off the
overvoltage-protection switching part to reduce the output voltage
of the DC-correction part by returning energy from the
DC-conversion part toward the AC power input part through the
inrush current limiting resistor when the output voltage of the
DC-conversion part is higher than a predetermined voltage.
[0013] According to an aspect of the invention, the DC-conversion
part comprises a pair of capacitors to be respectively charged with
positive and negative voltages from the AC power.
[0014] According to an aspect of the invention, the
overvoltage-protection switching part may comprise a pair of field
effect transistors (FETs).
[0015] According to an aspect of the invention, the controller
switches On/Off the overvoltage-protection switching part so as to
discharge at least one of the capacitors when a total voltage
applied to the capacitors reaches a predetermined overvoltage
limit.
[0016] According to an aspect of the invention, the sensor
comprises a comparator to sense an overvoltage applied to the
DC-conversion part.
[0017] According to an aspect of the invention, the inrush current
preventing part comprises an inrush current limiting resistor
between the AC power input part and the DC-conversion part and a
relay which selectively bypasses the inrush current limiting
resistor.
[0018] According to an aspect of the invention, the controller
switches the relay On when the total voltage applied to the
capacitors reaches a predetermined voltage limit, and switches the
relay Off when the total voltage applied to the capacitors reaches
the predetermined overvoltage limit.
[0019] According to another aspect of the invention, the foregoing
and/or other aspects of the invention may be achieved by providing
a method of controlling a motor power supply comprising an AC power
input part, a DC-conversion part which converts AC power from the
AC power input part into DC power, an inrush current limiting
resistor provided between the AC power input part and the
DC-conversion part, and an overvoltage-protection switching part
connected in parallel with an output of the DC-conversion part the
method comprising: gradually increasing an output voltage of the
DC-conversion part when power is initially supplied via the inrush
current limiting resistor; sensing the output voltage of the
DC-conversion part; and switching the overvoltage-protection
switching part alternately On/Off when the sensed voltage is higher
than a predetermined voltage so as to reduce the output voltage of
the DC-conversion part by returning energy toward the AC power
input part.
[0020] According to an aspect of the invention, the motor power
supply further comprises a relay connected in parallel with the
inrush current limiting resistor, and the method further comprises
switching the relay On when the output voltage of the DC-conversion
part reaches a predetermined voltage, so that the AC power input
part and the DC-conversion part are directly connected.
[0021] According to an aspect of the invention, the method further
comprises switching the relay Off when the output voltage of the
DC-conversion part is reduced by operation of the overvoltage
protection switching part.
BRIEF DESCRIPTION OF THE DRAWINGS
[0022] The above and/or other aspects and advantages of the present
invention will become apparent and more readily appreciated from
the following description of the embodiments, taken in conjunction
with the accompany drawings of which:
[0023] FIG. 1 is a circuit diagram of a motor power supply
according to the present invention;
[0024] FIGS. 2A-2F illustrate voltage and current waveforms at
junctions of the motor power supply according to the present
invention when power is initially supplied;
[0025] FIGS. 3A-3I illustrate voltage and current waveforms at
junctions of the motor power supply according to the present
invention when overvoltage is applied to a DC-conversion part of
FIG. 1;
[0026] FIGS. 4A and 4B are diagrams for explaining when a relay and
an overvoltage-protection switching part are switched according to
the present invention;
[0027] FIG. 5 is a comparative table showing a number of components
in the motor power supply according to the present invention and a
number of components of a conventional motor power supply shown in
FIG. 6; and
[0028] FIG. 6 is a circuit diagram of the conventional motor power
supply.
DESCRIPTION OF THE PREFERRED EMBODIMENT
[0029] Reference will now be made in detail to the embodiments of
the present invention, examples of which are illustrated in the
accompanying drawings, wherein like reference numerals refer to
like elements throughout.
[0030] FIG. 1 is a circuit diagram of a motor power supply 30
according to the present invention. As shown therein, the motor
power supply 30 comprises an AC power input part 1 having outputs
L1 and L2, a soft charging circuit 3 having a first end connected
to the output L1 of the AC power input part 1 and a second end
connected with a pair of overvoltage-protection switches 5a and 5b
which form an overvoltage-protection switching part 5, a
DC-conversion capacitor circuit 7 comprising capacitors C.sub.DC1
and C.sub.DC2 connected with the overvoltage-protection switching
part 5 in parallel, an inverter 16 connected with the DC-conversion
capacitor circuit 7 and which converts DC power into AC power
having a variable frequency to be supplied to a 3-phase motor 17,
and a controller 20 which controls the overvoltage-protection
switching part 5 so as to return a voltage applied to the
DC-conversion capacitor circuit 7 to the AC power input part 1 when
the voltage applied to the DC-conversion capacitor circuit 7 is
higher than a predetermined voltage. Further, the motor power
supply 30 comprises a voltage sensor 25, such as for example, a
comparator to sense the voltage applied to the DC-conversion
capacitor circuit 7 and to transmit sensed data to the controller
20.
[0031] The soft charging circuit 3 prevents an excessive inrush
current from flowing when power is initially supplied, and
comprises an inrush current limiting resistor 4 which limits the
inrush current, and a relay 2 which selectively bypasses the inrush
current limiting resistor 4.
[0032] The soft charging circuit 3 operates as follows. When power
is initially supplied, the relay 2 is in a state of being switched
Off, so that the limiting resistor 4 is not bypassed. Thus,
DC-conversion capacitors C.sub.DC1 and C.sub.DC2 are charged with a
positive voltage passing through the inrush current limiting
resistor 4 and a diode D1 and a negative voltage passing through
the inrush current limiting resistor 4 and a diode D2,
respectively. A total voltage applied to the pair of capacitors
C.sub.DC1 and C.sub.DC2 in the DC-conversion capacitor circuit 7
will be referred to as V.sub.PN. When V.sub.PN is equal to a
charging stop voltage V1, the relay 2 is switched On, so that the
inrush current limiting resistor 4 is bypassed and power from
output L1 of the AC power input part 1 is directly supplied to the
overvoltage-protection switching part 5 at a connection point
between the overload protection switch 5a and the overload
protection switch 5b.
[0033] According to the present invention, each of the
overload-protection switches 5a and 5b may comprise a field effect
transistors (FET), having a collector and an emitter connected with
a cathode and an anode, respectively, of a respective one of the
diodes D1 and D2. The diodes D1 and D2 serve as rectifier diodes to
charge the DC-conversion capacitor circuit 7 from the AC power
input part 1 and to prevent reverse-current due to the voltage
charged to the DC-conversion capacitor circuit 7 from being
returned to the AC power input part 1. The diodes D1 and D2 are
integrally formed with the overload-protection switches 5a and 5b,
respectively. Where the switches are FETs, the diodes D1 and D2 are
inherent diodes of the FETs.
[0034] The voltage sensor 25 senses whether the V.sub.PN applied to
the DC-conversion capacitor circuit 7 is higher than a
predetermined voltage (i.e., a critical overvoltage), and the
overvoltage-protection switching part 5 alternately switches On/Off
at least one of the overvoltage protection switches 5a and 5b so as
to return energy from the DC-conversion capacitor circuit 7 to the
AC power input part 1 when V.sub.PN is higher than the critical
overvoltage.
[0035] The controller 20 controls the relay 2 and the switches 5a
and 5b of the overvoltage-protection switching part 5 so as to
control V.sub.PN to be within an overvoltage protection band
between V.sub.H1 and V.sub.H2 (i.e., a hysteresis band,) as shown
in FIG. 3B. The controller 20 includes a logic circuit which
alternately outputs 0 and 1 signals to switch On and Off the
overvoltage-protection switching part 5, so that the overload
protection switches 5a and 5b are alternately switched On/Off,
thereby returning a regenerative power due to the motor 17 to the
AC power input part 1. That is, the controller 20 switches on the
overload protection switch 5a when a positive voltage (L1>L2) is
input, and switches on the overload protection switch 5b when a
negative voltage (L1<L2) is, thereby returning the regenerative
power charged in the DC-conversion capacitor circuit 7 by the motor
17 to the AC power input part 1.
[0036] The controller 20 controls the motor power supply 30 as
shown in FIG. 1 as follows. With reference to FIGS. 2E and 2F, when
power is initially supplied at t1, the controller 20 controls the
relay 2 to pass the power from the AC power input part 1 through
the inrush current limiting resistor 4 and the diodes D1 and D2 to
charge the DC-conversion capacitor circuit 7 with power supplied
via the inrush current limiting resistor 4. As shown in FIG. 2E,
the voltage V.sub.PN to the DC-conversion capacitor circuit 7
increases toward a voltage V1 at a rate determined by a value of
the limiting resistor 4 and a capacitance of the DC-conversion
capacitor circuit 7. When the controller 20 senses that the voltage
charged to the DC-conversion capacitor circuit 7 reaches a lower
limit voltage V1 at t2, the controller 20 switches the relay 2 On,
so that the input power is directly supplied to the DC-conversion
capacitor circuit 7, bypassing the limiting resistor 4. If the
voltage applied to the DC-conversion capacitor circuit 7 reaches an
upper limit voltage V2 as shown in FIG. 3B as the DC-conversion
capacitor circuit 7 is continuously charged with the power directly
supplied from the AC power input part 1, the controller 20 switches
the relay 2 Off at t3. Thereafter, If the voltage applied to the
DC-conversion capacitor circuit 7 is increased by the regenerative
energy due to the motor 17 and then reaches the overvoltage
protection band (V.sub.H1-V.sub.H2), the controller 20 alternately
switches the switches 5a and 5b On/Off (e.g., t4/t4a, t5/t5a,
t6/t6a and t7/t7a of FIG. 3F) connected with the DC-conversion
capacitor circuit 7, thereby returning the regenerative energy to
the AC power input part 1 via the inrush current limiting resistor
4.
[0037] FIGS. 2A-2F illustrates voltage and current waveforms at
junctions of the motor power supply when the power is initially
supplied. As shown in FIG. 2A, the power through the AC power input
part 1 (V.sub.L1-L2) has a sinusoidal waveform which alternates
between a positive value and a negative value. When the power is
initially supplied through the AC power input part 1 beginning at
t1, the relay 2 is in the state of being switched Off as shown in
FIG. 2F, so that an AC current flows via the inrush current
limiting resistor 4. As the AC current flows, the DC-conversion
capacitors C.sub.DC1 and C.sub.DC2 are gradually charged with an
electric charge, so that the voltage applied to each of the
capacitors C.sub.DC1 and C.sub.DC2 is gradually increased as shown
in FIGS. 2B and 2C, respectively, where V.sub.P-L2 is the voltage
to the capacitor C.sub.DC1 and V.sub.L2-N is the voltage to the
capacitor C.sub.DC2. A decreasing current I.sub.s flowing during
charging of the capacitors C.sub.DC1 and C.sub.DC2 is shown in FIG.
2D. When the capacitors C.sub.DC1 and C.sub.DC2 are fully charged
according to the input voltage V.sub.L1-L2, the voltage to the
DC-conversion capacitor circuit 7, i.e., the series combination of
capacitors C.sub.DC1 and C.sub.DC2, is about double a peak value of
the input voltage V.sub.L1-L2, or about a peak to peak value of the
input voltage V.sub.L1-L2.
[0038] The controller 20 switches the relay 2 On when the voltage
applied to the DC-conversion capacitor circuit 7 reaches the lower
limit voltage V1 (t2 in FIGS. 2E and 2F). When the relay 2 is
switched on, the AC power input part 1 and the DC-conversion
capacitor circuit 7 are directly connected and the DC-conversion
capacitor circuit 7 is more rapidly charged due to bypassing the
limiting resistor 4. At this time, the total voltage V.sub.PN
applied to the pair of capacitors C.sub.DC1 and C.sub.DC2 may have
an overshoot waveform because of the more rapid charging and some
discharging may be necessary.
[0039] FIGS. 3A-3I illustrate voltage and current waveforms at
junctions of the motor power supply when overvoltage is applied to
the DC-conversion capacitor circuit 7. When the regenerative
energy, which is generated by the motor 17, passes through the
inverter 16 and is applied to the DC-conversion capacitor circuit
7, causes the total voltage V.sub.PN to be increased and to reach
the upper voltage limit V2, the controller 20 switches the relay 2
Off, as indicated by t3 of FIGS. 3B and 3D. While a positive going
voltage is supplied as the voltage V.sub.L1-L2 in the state that
the relay 2 is switched Off, the moment when total voltage V.sub.PN
reaches the upper overvoltage limit V.sub.H2 of the hysteresis
band, the controller 20 switches the switch 5a On (e.g., t4 and t6
of FIG. 3G). As the first switch 5a is switched on, the overvoltage
applied to the DC-conversion capacitor circuit 7 is gradually
discharged, and a current due to discharging flows toward the AC
power input part 1 (e.g., t4 and t6 of FIG. 3I). In other words,
the regenerated energy is returned to the AC power input part 1,
thereby discharging the overvoltage applied to the DC-conversion
capacitor circuit 7. Thereafter, as the overvoltage applied to the
DC-conversion capacitor circuit 7 is discharged, when total voltage
V.sub.PN reaches a lower overvoltage limit V.sub.H1 of the
hysteresis band (V.sub.H1-V.sub.H2), the controller 20 switches the
switch 5a Off (e.g., t4a and t6a of FIG. 3G).
[0040] Further, while a negative going voltage is supplied as the
voltage V.sub.L1-L2, the moment when the total voltage V.sub.PN
reaches the upper overvoltage limit V.sub.H2 of the hysteresis band
(V.sub.H1-V.sub.H2), the controller 20 switches the switch 5b On
(e.g., t5 and t7 of FIG. 3H). As the switch 5b is switched On, the
overvoltage applied to the DC-conversion capacitor circuit 7 is
gradually discharged, and a current due to the discharging flows
toward the AC power input part 1 (e.g. at t5 and t7 of FIG. 3I). In
other words, the regenerated energy is returned to the AC power
input part 1. Thereafter, as the overvoltage applied to the
DC-conversion capacitor circuit 7 is discharged, when the total
voltage V.sub.PN reaches the lower overvoltage limit V.sub.H1 of
the hysteresis band (V.sub.H1-V.sub.H2), the controller 20 switches
the switch 5b Off (t5a and t7a of FIG. 3H).
[0041] Thereafter, when the total voltage V.sub.PN decreases
because the regenerative energy generated by the motor 17 is
returned to the AC power input part 1 and the total voltage
V.sub.PN falls below the upper voltage limit V2, the relay 3 is
again switched On to bypass the limiting resistor 4 (e.g., t8 of
FIG. 3D).
[0042] As the total voltage V.sub.PN applied to the DC-conversion
capacitor circuit 7 is decreased and reaches the upper limit
voltage V2, the controller 20 switches the relay 2 On (e.g., t8 of
FIG. 3D), so that the AC power input part 1 and the DC-conversion
capacitor circuit 7 are again directly connected. Then, the direct
connection causes a supplementary voltage to be applied to the
DC-conversion capacitor circuit 7, thereby causing the total
voltage V.sub.PN to have the overshoot waveform.
[0043] As shown in of FIG. 3I, when a current waveform of the
regenerative power bypassed through the inrush current limiting
resistor 4 has a same positive or negative sign as a current
waveform of the power inputted through the AC power input part 1,
energy will be regenerated. Oppositely, when both current waveforms
are different from each other in a positive or negative sign,
energy will be lost.
[0044] As shown in FIG. 3, when total voltage V.sub.PN is higher
than a sum of half-wave rectified positive (FIG. 3B) and negative
(FIG. 3C) input voltages, the input current I.sub.s becomes 0 (FIG.
3I). Therefore, when the total voltage V.sub.PN exceeds the upper
limit voltage V2, a voltage spike is not generated when the relay 2
is switched from On to Off. Hence, an additional snubber circuit or
a current channel is not needed.
[0045] FIGS. 4A and 4B are diagrams for explaining when the relay 2
and the overvoltage-protection switching part 5 according to the
present invention are turned On. As shown in FIG. 4A, the
controller 20 switches the relay 2 Off while the voltage V.sub.PN
applied to the DC-conversion capacitor circuit 7 is below the
voltage V1, switches the relay 2 On while the voltage V.sub.PN is
within the voltage band between V1 and V2, and switches the relay 2
Off when the voltage V.sub.PN VPN exceeds the voltage V2. The
controller switches the overvoltage-protection switching part 5 On
to keep the total voltage V.sub.PN applied to the DC-conversion
capacitor circuit 7 within the overvoltage band between V.sub.H1
and V.sub.H2, i.e., enables the overvoltage-protection switching
part 5 when the total voltage V.sub.PN is greater than V.sub.H1 so
that the DC-conversion capacitor circuit 7 begins to be discharged
when the total voltage V.sub.PN increases to V.sub.H2 and stops the
discharging when the total voltage V.sub.PN decreases to V.sub.H1
while the DC-conversion capacitor circuit 7 is being discharged by
the overvoltage-protection part 5. During operation of the
overvoltage switching part 5, the switch 5a is switched
synchronously with a positive sign of V.sub.L1-L2 as shown in FIG.
4B and the switch 5b is switched synchronously with a negative sign
of V.sub.L1-L2.
[0046] FIG. 5 is a comparative table showing a number of components
used in the motor power supply according to the present invention
and a number of components used in the conventional motor power
supply shown in FIG. 6. As shown in FIG. 5, a total element number
of components of the motor power supply according to the present
invention is reduced by three as compared with the conventional
motor power supply shown in FIG. 6. The numbers shown in FIG. 5 are
exclusive of the components shown in the inverters 16 and 116,
which have a same number of components. The diodes D1 and D2 shown
in FIG. 1 are not included in the component count since the diodes
D1 and D2 are integrally formed with or inherent in the switches 5a
and 5b, respectively.
[0047] In the motor power supply according to the present
invention, while the motor operates or is working, if the
regenerative energy generated by the inverter causes the
DC-conversion circuit to be overloaded, the overvoltage-protection
switching part is alternately switched On and Off. Therefore, the
overvoltage applied to the DC-conversion circuit is returned toward
the AC power input part, so that some regenerative energy is
regenerated and some regenerative energy is dissipated as heat
energy by the inrush current limiting resistor.
[0048] As described above, the present invention provides a motor
power supply and a method of controlling the same, in which a
regenerative energy causing a DC-conversion circuit to be
overloaded is used as an input energy, thereby enhancing energy
efficiency.
[0049] Although a few embodiments of the present invention have
been shown and described, it will be appreciated by those skilled
in the art that changes may be made in these embodiments without
departing from the principles and spirit of the invention, the
scope of which is defined in the appended claims and their
equivalents.
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